Setting a read/write host for m0n0wall development.
It's what I've done to install a developement box for m0n0wall on an
old Pentium. There's 2 disk.
First one is the build system, a full FreeBSD 5.x install, and the second
is a small disk, used to run m0n0wall.

Convention:
${DISK}: device of m0n0wall disk
${DESTDIR}: mount point of m0n0wall disk.
${WRKDIR}: where you work ;)

On the host system:
1. Preparing the disk 
  * Run sysinstall -> configure -> Fdisk
    select m0n0wall dedicated disk
    Use entire disk and choose Standard boot loader.
  * Quit sysintall and run:
	 bsdlabel -w ${DISK}s1 auto
  newfs /dev/${DISK}s1a
  mount /dev/${DISK}s1a ${DESTDIR}/

2. Populate base install:
   * fetch generic-pc images and rootfs from m0n0wall.
   * extract kernel and /boot from generic-pc image (gunzip it, mdconfig'
     it and mount it). Copy them to ${WRKDIR}.
   tar pxzvf  ${WRKDIR}/rootfs-1.2b7.tar.gz -C ${DESTDIR}/
   cp ${WRKDIR}/kernel ${DESTDIR}/boot/kernel/
   cp -Rvf ${WRKDIR}/boot/* ${DESTDIR}/boot/

3. Make it boot on non-mfs'd root
   * edit ${DESTDIR}/boot/loader.rc
   * remove ^load lines
   * add "set vfs.root.mountfrom=ufs:/dev/ad0s1a"
   * edit ${DESTDIR}/etc/rc
     add
	# remount /
	ROOTDEV=/dev/$(/sbin/sysctl -n kern.rootdev)
	mount $ROOTDEV /
	echo $ROOTDEV / ufs rw 1 1 > /etc/fstab
     to etc/rc before "# make some directories in /var" line

   mkdir ${DESTDIR}/cf/conf
   cp ${DESTDIR}/conf.default/config.xml ${DESTDIR}/cf/conf/

4. Add editors and ssh stuff
   - installing ee/vi
   cp -p /lib/libncurses.so.5 ${DESTDIR}/lib/
   cp -p /usr/bin/vi ${DESTDIR}/usr/bin/
   cp -p /usr/bin/ee ${DESTDIR}/usr/bin/
   mkdir ${DESTDIR}/usr/share/misc
   cp -p /etc/termap ${DESTDIR}/etc
   cp -p /usr/share/misc/termap.db /usr/share/misc/
 
   - install ssh stuff
   fetch http://www.xs4all.nl/~fredmol/m0n0/m0n0-dropbear-ssh.tgz
   mkdir dropbear
   (still in ${WRKDIR})
   tar xzf m0n0-dropbear-ssh.tgz -C dropbear/
   ###cd ${DESTDIR}
   cp -p /usr/sbin/pw ${DESTDIR}/usr/sbin/
   cd ${WRKDIR}/dropbear/install-root
   rm etc/rc.firmware usr/sbin/dropbear usr/bin/dropbearkey
   mkdir ${DESTDIR}/etc/dropbear
   mv etc/inc/ext/dropbear ${DESTDIR}/etc/inc
   cd ${WRKDIR}
   - compile dropbear for our system
   cd /usr/ports/security/dropbear
   make install clean
   install -s -m 0555 -o root -g wheel /usr/local/sbin/dropbear \
                ${DESTDIR}/usr/sbin/
   install -s -m 0555 -o root -g wheel /usr/local/bin/dropbearkey  \
                ${DESTDIR}/usr/bin/

Reboot to your new m0n0wall system.
You can now log in via SSH and add modify files.
to copy file I use :
	"cat </path/to/file> | ssh <monobox> "cat - > </path/to/file>"
on m0n0wall box "chmod +x </path/to/file>"

Enjoy...